Word-level blind diarization of recorded calls with arbitrary number of speakers

ABSTRACT

Disclosed herein are methods of diarizing audio data using first-pass blind diarization and second-pass blind diarization that generate speaker statistical models, wherein the first pass-blind diarization is on a per-frame basis and the second pass-blind diarization is on a per-word basis, and methods of creating acoustic signatures for a common speaker based only on the statistical models of the speakers in each audio session.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. patent application Ser.No. 15/006,572, now issued U.S. Pat. No. 9,875,742, which claimspriority to U.S. Provisional Patent Applications Nos. 62/107,702 and62/107,751, both filed Jan. 26, 2015, the contents of which are eachincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure is related to the field of automatedtranscription. More specifically, the present disclosure is related todiarization of audio data with an arbitrary number of speakers and thecreation of acoustic signatures for a speaker from multiple recordedsessions.

BACKGROUND

Speech transcription and speech analytics of audio data may be enhancedby a process of diarization wherein audio data that contains multiplespeakers is separated into segments of audio data typically to a singlespeaker. While speaker separation in diarization facilitates latertranscription and/or speech analytics, the identification of ordiscrimination between identified speakers can further facilitate theseprocesses by enabling the association of context and information inlater transcription and speech analytics processes specific to anidentified speaker.

Previous diarization solutions for example of a recorded telephoneconversation of a customer service application assume two speakers. Thetwo speakers may exemplarily be a customer and an agent (i.e. acustomer-service representative) in a call center. The two-speakerassumption greatly simplifies the blind-diarization task. However, manycalls may have a more complex structure. Some calls may feature only asingle speaker, exemplarily a recorded message or an IVR message. Othercalls may contain additional “speech-like” segments. For example, thesesegments may include background talks. Still other examples of complexcalls include calls with three speakers or more such as conference callsor calls in which one or more speakers are replaced by another speaker.

Prior blind diarization solutions have relied on a first-pass filteringwhich may fail to accurately filter out non-speech segments, e.g. noisesor music, resulting in too many speakers being created. Additionally,prior blind diarization processes have relied on classification beingperformed solely on a per-frame basis and thus may fail to detect shortutterances that are interleaved with longer utterances of anotherspeaker.

Therefore, a blind-diarization algorithm that does not assume any priorknowledge on the number of speakers, that does not solely rely onper-frame classification, and performs robustly on calls with arbitrarynumber of speakers is achieved in embodiments as disclosed herein.

Building of acoustic signatures for a common speaker can be a problem.Given a set of recorded sessions (telephone calls, recordings from ameeting room, etc.). Namely, constructing a statistical model that canbe used to detect the presence of that speaker in other recordedsessions. In a call-center environment, such a common speaker may be acustomer service representative—for which typically there are hundredsof available sessions—or a customer making repeating calls to thecall-center. In case of recorded material from meeting rooms, we may beinterested in identifying a specific person participating in some ofthese meetings.

Given recorded audio from all sessions along with markers that indicatethe presence of a common speaker within each session (start time and endtime of each utterance of that speaker), the solution for creating anacoustic signature for a speaker can be quite straightforward. Forexample, it is possible to extract acoustic features from all relevantutterances and construct a statistical model that can be used as anacoustic label for the speaker. This can be done using simpleclassifiers a GMM, or more advanced techniques such as I-vectors.

However, storing and processing audio data from hundreds of recordedsessions may be very time consuming and pose a burden on the network ifthese sessions needs to be collected from several servers to a singlelocation.

Therefore, a method that creates an acoustic signature for a commonspeaker based only on statistical models of the speakers in each sessionis further disclosed herein.

SUMMARY

An exemplary embodiment of a method of diarization of audio dataincludes identifying non-speech segments in the audio using avoice-activity-detector (VAD) and segmenting audio data into a pluralityof utterance that are separated by the identified non-speech segments.Each utterance is represented as an utterance model representative of aplurality of feature vectors of each utterance. The utterance models areclustered. A plurality of speaker models are constructed from theclustered utterance models. A hidden Markov model (HMM) of the pluralityof speaker models is constructed. A sequence of identified speakermodels that best corresponds to the utterances of the audio data isdecoded. Each VAD segment is decoded using a large-vocabulary continuousspeech recognition (LVCSR) decoder, wherein the LVCSR decoder outputswords and non-speech symbols. The sequence of output words andnon-speech symbols from the LVCSR decoder is analyzed, whereinnon-speech parts are discarded and the segment is refined resulting insub-segments comprising words. A second plurality of speaker models areconstructed by feeding the resulting sub-segments into a clusteringalgorithm. A second HMM of the second plurality of speaker models isconstructed. A best path corresponding to the sequence of output wordsin the second HMM is decoded by applying a Viterbi algorithm thatperforms word-level segmentation

In an exemplary embodiment of a method of creating an acoustic signaturefor a speaker from multiple sessions, a training set containing a numberof recorded audio sessions is obtained, wherein each session includes aplurality of speaker models, wherein each speaker model is characterizedby its occupancy which is proportion to the number of feature vectorsused to construct the speaker model, wherein the speaker models areGaussian mixture models (GMMs). The plurality of speaker models areclassified to identify a set of common speaker GMMs and a set of genericspeaker GMMs, wherein the classifying includes constructing anundirected similarity graph having vertices corresponding to theplurality of speaker models of all the recorded audio session in thetraining set and classifying the plurality of speaker models accordingto a degree of their corresponding vertex in the undirected similaritygraph. An acoustic signature is generated by at least: constructing asuper-GMM for the set of common speaker GMMs, and constructing asuper-GMM for the set of generic speaker GMMs by generating a large setof random vectors and training a GMM over these random vectors, whereinthe acoustic signature for the common speak is given as the super-modelpair of the two constructed super-GMMs.

The details of one or more embodiments of the disclosure are set forthin the accompanying drawings and the description below. Other features,objects, and advantages of the disclosure will be apparent from thedescription, drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart that depicts an embodiment of a method oftranscription using blind diarization.

FIG. 2 is a flow chart that depicts an embodiment of creating and usingan acoustic voiceprint model.

FIG. 3 is a system diagram of an exemplary embodiment of a system fordiarization of audio data.

FIG. 4 is a flow chart that depicts an exemplary embodiment of a methodof blind diarization with an arbitrary number of speakers.

FIG. 5 depicts an exemplary embodiment of a state diagram modeling aconversation between N speakers.

FIG. 6 is a flow chart that depicts an exemplary embodiment of moredetailed processes carried out during embodiments of a method of blinddiarization with an arbitrary number of speakers

FIG. 7 is a flow chart that depicts an exemplary embodiment ofperforming a second-pass blind diarization.

FIG. 8 is a flow chart that depicts an exemplary embodiment of a methodof creating acoustic signatures for a speaker from multiple recordedaudio sessions that is based only on statistical models of the speakersin each of a set of recorded sessions.

DETAILED DISCLOSURE

Speech transcription of audio data, which may include streaming orpreviously recorded audio data, is enhanced by diarization wherein aspeaker identity is identified and associated with transcribed speech. Aspeaker diarization system and method is aimed at identifying thespeakers in a given call and associating each transcribed speech segmentwith an identified speaker. Speaker diarization thus enables theseparation of speakers in the transcription of audio data.

Embodiments of a diarization process disclosed herein include a firstoptional step of a speech-to-text transcription of audio data to bediarized. Next, a “blind” diarization of the audio data is performed.The audio data is exemplarily a .WAV file, but may also be other typesof audio data in a pulse code modulated (PCM) format or linear pulsecode modulated (LPCM) format. Furthermore, the audio data is exemplarilya mono audio file; however, it is recognized that embodiments of thesystems and methods as disclosed herein may also be used with stereoaudio data. The blind diarization receives the audio file and optionallythe automatically generated transcript. This diarization ischaracterized as “blind” as the diarization is performed prior to anidentification of the speakers. In an exemplary embodiment of a customerservice call, the “blind diarization” may only cluster the audio datainto speakers while it may still be undetermined which speaker is theagent and which speaker is the customer.

The blind diarization is followed by a speaker diarization wherein avoiceprint model that represents the speech and/or information contentof an identified speaker in the audio data is compared to the identifiedspeech segments associated with the separated speakers. Through thiscomparison, one speaker can be selected as the known speaker, while theother speaker is identified as the other speaker. In an exemplaryembodiment of customer service interactions, the customer agent willhave a voiceprint model as disclosed herein which is used to identifyone of the separated speaker as the agent while the other speaker is thecustomer.

The identification of segments in an audio file, such as an audio streamor recording (e.g. a telephone call that contains speech) can facilitateincreased accuracy in transcription, diarization, speaker adaption,and/or speech analytics of the audio file. An initial transcription,exemplarily from a fast speech-to-text engine, can be used to moreaccurately identify speech segments in an audio file, such as an audiostream or recording, resulting in more accurate diarization and/orspeech adaptation.

FIGS. 1 and 2 are flow charts that respectively depict exemplaryembodiments of method 100 of transcription using blind diarization and amethod 200 of creating and using an acoustic voiceprint model. FIG. 4depicts an exemplary embodiment of a method 400 of blind diarizationwith an arbitrary number of speakers. FIG. 5 depicts an exemplaryembodiment of more detailed method 500 as may be incorporated into anembodiment of a method of blind diarization. FIG. 7 depicts an exemplaryembodiment of a method 700 of performing second-pass blind diarization.FIG. 8 depicts an exemplary embodiment of a method 800 of creatingacoustic signatures for a speaker from multiple recorded audio sessionsthat is based only on statistical models of the speakers in each of aset of recorded sessions. FIG. 3 is a system diagram of an exemplaryembodiment of a system 300 which may carry out and implement any methods100, 200, 400, 500, 700, and 800 as described in further detail herein.The system 300 is generally a computing system that includes aprocessing system 306, storage system 304, software 302, communicationinterface 308 and a user interface 310. The processing system 306 loadsand executes software 302 from the storage system 304, including asoftware module 330. When executed by the computing system 300, softwaremodule 330 directs the processing system 306 to operate as described inherein in further detail in accordance with the methods 400, 500, 700,and 800 and in additional embodiments, methods 100 and 200.

Although the computing system 300 as depicted in FIG. 3 includes onesoftware module in the present example, it should be understood that oneor more modules could provide the same operation. Similarly, while thedescription as provided herein refers to a computing system 300 and aprocessing system 306, it is to be recognized that implementations ofsuch systems can be performed using one or more processors, which may becommunicatively connected, and such implementations are considered to bewithin the scope of the description.

The processing system 306 can comprise a microprocessor and othercircuitry that retrieves and executes software 302 from storage system304. Processing system 306 can be implemented within a single processingdevice but can also be distributed across multiple processing devices orsub-systems that cooperate in executing program instructions. Examplesof processing system 306 include general purpose central processingunits, application specific processors, and logic devices, as well asany other type of processing device, combinations of processing devices,or variations thereof.

The storage system 304 can comprise any storage media readable byprocessing system 306, and capable of storing software 302. The storagesystem 304 can include volatile and non-volatile, removable andnon-removable media implemented in any method or technology for storageof information, such as computer readable instructions, data structures,program modules, or other data. Storage system 304 can be implemented asa single storage device but may also be implemented across multiplestorage devices or sub-systems. Storage system 304 can further includeadditional elements, such as a controller capable of communicating withthe processing system 306.

Examples of storage media include random access memory, read onlymemory, magnetic discs, optical discs, flash memory, virtual memory andnon-virtual memory, magnetic sets, magnetic tape, magnetic disc storageor other magnetic storage devices, or any other medium which can be usedto store the desired information and that may be accessed by aninstruction execution system, as well as any combination or variationthereof, or any other type of storage medium. In some implementations,the storage media can be a non-transitory storage media. In someimplementations, at least a portion of the storage media may betransitory.

User interface 310 can include a mouse, a keyboard, a voice inputdevice, a touch input device for receiving a gesture from a user, amotion input device for detecting non-touch gestures and other motionsby a user, and other comparable input devices and associated processingelements capable of receiving user input from a user. Output devicessuch as a video display or graphical display can display an interfacefurther associated with embodiments of the system and method asdisclosed herein. Speakers, printers, haptic devices and other types ofoutput devices may also be included in the user interface 310.

As described in further detail herein, the computing system 300 receivesand transmits data through the communication interface 308. Inembodiments, the communication interface 308 operates to send and/orreceive data to/from other devices to which the computing system 300 iscommunicatively connected. In the computing 300, audio data 320 isreceived at the communication interface 308. The audio data 320 may bean audio recording or a conversation, which may exemplarily be betweenan unknown number of speakers, although the audio recording may be anyof a variety of other audio records, including two speakers, multiplespeakers, a single speaker, or an automated or recorded auditorymessage. In still further embodiments, the audio data may be streamingaudio data received in real time or near-real time by the computingsystem 300. In a further exemplary embodiment, the audio data mayexemplarily be a .WAV file, but may also be other types of audio orvideo files, for example, pulse code modulated (PCM) formatted audio,and more specifically, linear pulse code modulated (LPCM) audio files.Furthermore, the audio data is exemplarily a mono audio file; however,it is recognized that embodiments of the method disclosed herein mayalso be used with stereo audio files. One feature of the methodsdisclosed herein are that speaker separation and diarization can beachieved in mono audio files where stereo speaker separation techniquesare not available.

In still further embodiments, the audio data 320 is received at thecomputing system 300 at the communication interface 308. The processingsystem 306 further obtaining at least one acoustic model, which may befurther received at the communication interface 308, or may be stored atthe storage system 304. The processing system 306, upon execution of theapplication module 330 diarizes the audio data in the manner asdescribed in further detail herein. In exemplary embodiments, thediarized audio data may be output from the communication interface 308to another computing device. In other embodiments, the processing system206 further operates to transcribe the diarized audio data in order toproduce a diarized transcript 350. The diarized transcript 350 may betransmitted from the computing system 300 via the communicationinterface 308 to another computing device or may be exemplarilypresented to a user at the user interface 310, which may exemplarily bea graphical display.

FIG. 1 is a flow chart that depicts an exemplary embodiment of a method100 of diarization of audio data. The method 100 beings at theacquisition of audio data 102. As described above, the audio dataacquired at 102 may exemplarily be real-time or streaming audio data ofmay be previously acquired and stored audio data.

In embodiments, the audio data 102 further comprises or is associated tometadata 108. The metadata 108 can exemplarily include an identificationnumber for one or more of the speakers in the audio data 102. Inalternative embodiments, the metadata 108 may provide informationregarding context or content of the audio data 102, including a topic,time, date, location etc. In the context of a customer service callcenter, the metadata 108 provides a customer service agentidentification.

In an embodiment, the audio data 102 and the metadata 108 are providedto a speech-to-text (STT) server 104, which may employ any of a varietyof method of techniques for automatic speech recognition (ASR) to createan automated speech-to-text transcription 106 from the audio file. Thetranscription performed by the STT server at 104 can exemplarily be alarge-vocabulary continuous speech recognition (LVCSR) and the audiodata 102 provided to the STTserver 104 can alternatively be a previouslyrecorded audio file or can be streaming audio data obtained from anongoing communication between two speakers. In an exemplary embodiment,the STT server 104 may use the received metadata 108 to select one ormore models or techniques for producing the automated transcriptioncased upon the metadata 108. In a non-limiting example, anidentification of one of the speakers in the audio data can be used toselect a topical linguistic model based upon a content area associatedwith the speaker. In addition to the transcription 106 from the STTserver 104, STT server 104 may also output time stamps associated withparticular transcription segments, words, or phrases, and may alsoinclude a confidence score in the automated transcription. Thetranscription 106 may also identify homogeneous speaker speech segments.Homogenous speech segments are those segments of the transcription thathave a high likelihood of originating from a single speaker. The speechsegments may exemplarily be phonemes, words, or sentences.

After the transcription 106 is created, both the audio data 102 and thetranscription 106 are used for a blind diarization at 110. However, itis to be recognized that in alternative embodiments, the blinddiarization may be performed without the transcription 106 and may beapplied directly to the audio data 102. In such embodiments, thefeatures at 104 and 106 as described above may not be used. Thediarization is characterized as blind as the identities of the speakers(e.g. agent, customer) are not known at this stage and therefore thediarization 110 merely discriminates between a first speaker (speaker 1)and a second speaker (speaker 2), or more. Additionally, in someembodiments, those segments for which a speaker cannot be reliablydetermined may be labeled as being of an unknown speaker.

An embodiment of the blind diarization at 110 receives the mono audiodata 102 and the transcription 106 and begins with the assumption thatthere are two main speakers in the audio file. The blind diarizationseparates the audio data into frames as disclosed in further detailherein and separates the audio data into frames for diarization usingtwo techniques. The first techniques uses energy envelopes in the audiofile, or other audio analysis techniques as disclosed herein to identifysegments attributable to separate speakers. The blind diarizationprocess then filters out non-speech frames. In an exemplary embodiment,this may be performed by removing a frame if the dynamic energy range inthe frame is below a predetermined threshold. Alternatively, or anaddition, frames may be removed if the high frequency energy in theframe falls outside of a predetermined pass band for high frequencyenergy in a frame.

After the audio file has been segmented based upon the energy envelopeanalysis, homogeneous speaker segments from 106 are identified in theaudio file. Then, long homogeneous speaker segments can be split intosub-segments if long silent intervals are found within a single segment.The sub-segments are selected to avoid splitting the long speakersegments within a word. The transcription information in the informationfile 106 can provide context to where individual words start and end.After the audio file has been segmented based upon both the audio file102 and the information file 106, the identified segments are clusteredinto speakers (e.g. speaker 1, speaker 2, speaker N).

In an embodiment, the blind diarization uses voice activity detection(VAD) to segment the audio data 102 into utterances or short segments ofaudio data with a likelihood of emanating from a single speaker. In anembodiment, the VAD segments the audio data into utterances byidentifying segments of speech separated by segments of non-speech on aframe-by-frame basis. Context provided by the transcription 106 canimprove the distinction between speech and not speech segments. In theVAD, an audio frame may be identified as speech or non-speech based upona plurality of characteristics or probabilities exemplarily based uponmean energy, band energy, peakiness, or residual energy; however, itwill be recognized that alternative characteristics or probabilities maybe used in alternative embodiments.

Embodiments of the blind diarization 110 may further leverage thereceived metadata 108 to select an acoustic voiceprint model 116, from aplurality of stored acoustic voiceprint models as well be described infurther detail herein. Embodiments that use the acoustic voiceprintmodel in the blind diarization 110 can improve the clustering of thesegmented audio data into speakers, for example by helping to clustersegments that are otherwise indeterminate, or “unknown.”

The blind diarization at 110 results in audio data of separated speakersat 112. In an example, the homogeneous speaker segments in the audiodata are tagged as being associated with a first speaker or a secondspeaker. As mentioned above, in some embodiments, in determinatesegments may be tagged as “unknown” and audio data may have more thantwo speakers tagged.

At 114 a second diarization, “speaker” diarization, is undertaken toidentify the tagged speakers. In a customer service context, this mayinclude the identification of which speaker is the customer serviceagent.

A variety of techniques may be used to identify the agent, includingacoustical matching techniques of speech transcription and text analysistechniques. In an embodiment, an agent model, which can be derived in avariety of manners or techniques, may be compared to the homogeneousspeaker in the audio file segments assigned to speaker 1 and thencompared to the homogeneous speaker segments in the audio file assignedto speaker 2 to determine which combination of homogenous speakersegments has a greater likelihood of matching the agent model. Thehomogeneous speaker segments tagged in the audio file as being thespeaker that is most likely the agent based upon the comparison of theagent model are tagged as the agent and the homogeneous speaker segmentstagged in the audio file as being the other speaker are tagged as thecustomer.

A transcript resulting from automatic speech-to-text transcriptionprovides information on speech segments such as phonemes, words, orsentences. These speech segments can then be clustered into groups ofspeech segments that have a high likelihood of emanating from the samespeaker. These clustered segments can be used to discriminate betweenspeakers in the diarization process. The identification and use ofidentifiable speech segments as the input for the diarization canfurther facilitate filtering out noise and other non-speech segmentsthat can interfere with the diarization process. In another embodiment,features or characteristics of the audio files of clustered as each ofthe speakers are compared to speech models of known agents, customers,or other speakers. From this comparison, one or both of the speakers maybe identified.

In a still further exemplary embodiment of a customer serviceinteraction, the metadata 108 identifies a customer service agentparticipating in the recorded conversation and the other speaker isidentified as the customer. An acoustic voiceprint model 116, which canbe derived in a variety of manners or techniques as described in moredetail herein, is compared to the homogeneous speaker audio datasegments assigned to the first speaker and then compared to thehomogeneous speaker audio data segments assigned to the second speakerto determine which separated speaker audio data segments have a greaterlikelihood of matching the acoustic voiceprint model 116. At 118, thehomogeneous speaker segments tagged in the audio file as being thespeaker that is most likely the agent based upon the comparison of theacoustic voiceprint model 116 are tagged as the speaker identified inthe metadata and the other homogeneous speaker segments are tagged asbeing the other speaker.

At 120, the diarized and labeled audio data from 118 again undergoes anautomated transcription, exemplarily performed by a STT server or otherform of ASR, which exemplarily may be LVCSR. With the additional contextof both enhanced identification of speaker segments and clustering andlabeling of the speaker in the audio data, an automated transcription122 can be output from the transcription at 120 through the applicationof improved algorithms and selection of further linguistic or acousticmodels tailored to either the identified agent or the customer, oranother aspect of the customer service interaction as identified throughthe identification of one or more of the speakers in the audio data.This improved labeling of the speaker in the audio data and theresulting transcription 122 can also facilitate analytics of the spokencontent of the audio data by providing additional context regarding thespeaker, as well as improved transcription of the audio data.

It is to be noted that in some embodiments, the acoustic voice prints asdescribed herein may be used in conjunction with one or more linguisticmodels, exemplarily the linguistic models as disclosed and applied inU.S. patent application Ser. No. 14/084,976, which is incorporatedherein by reference. In such combined embodiments, the speakerdiarization may be performed in parallel with both a linguistic modeland an acoustic voice print model and the two resulting speakerdiarization are combined or analyzed in combination in order to providean improved separation of the audio data into known speakers. In anexemplary embodiment, if both models agree on a speaker label, then thatlabel is used, while if the analysis disagrees, then an evaluation maybe made to determine which model is the more reliable or more likelymodel based upon the context of the audio data. Such an exemplaryembodiment may offer the advantages of both acoustic and linguisticmodeling and speaker separation techniques.

In a still further embodiment, the combination of both an acousticvoiceprint model and a linguistic model can help to identify errors inthe blind diarization or the speaker separation phases, exemplarily byhighlighting the portions of the audio data above within which the twomodels disagree and providing for more detailed analysis on those areasin which the models are in disagreement in order to arrive at thecorrect diarization and speaker labeling. Similarly, the use of anadditional linguistic model may provide a backup for an instance whereinan acoustic voiceprint is not available or identified based upon thereceived metadata. For example, this situation may arrive when there isinsufficient audio data regarding a speaker to create an acousticvoiceprint as described in further detail herein.

Alternatively, in embodiments, even if the metadata does not identify aspeaker, if an acoustic voiceprint exists for a speaker in the audiodata, all of the available acoustic voiceprints may be compared to theaudio data in order to identify at least one of the speakers in theaudio data. In a still further embodiment, a combined implantation usinga linguistic model and an acoustic model may help to identify anincongruity between the received metadata, which may identify onespeaker, while the comparison to that speaker's acoustic voiceprintmodel reveals that the identified speaker is not in the audio data. Inone non-limiting example, in the context of a customer serviceinteraction, this may help to detect an instance wherein a customerservice agent enters the wrong agent ID number so that corrective actionmay be taken. Finally, in still further embodiments the use of acombination of acoustic and linguistic models may help in theidentification and separation of speakers in audio data that containmore than two speakers, exemplarily, one customer service agent and twocustomers; two agents and one customer; or an agent, a customer, and anautomated recording such as a voicemail message.

FIG. 2 is a flow chart that depicts an embodiment of the creation anduse of an acoustic voiceprint model exemplarily used as the acousticvoiceprint model 116 in FIG. 1. Referring back to FIG. 2, the method 200is divided into two portions, exemplarily, the creation of the acousticvoiceprint model at 202 and the application or use of the acousticvoiceprint model at 204 to label speakers in an audio file. In anexemplary embodiment of a customer service interaction, the acousticvoiceprint model is of a customer service agent and associated with anagent identification number specific to the customer service agent.

Referring specifically to the features at 202, at 206 a number (N) offiles are selected from a repository of files 208. The files selected at206 all share a common speaker, exemplarily, the customer service agentfor which the model is being created. In an embodiment, in order to makethis selection, each of the audio files in the repository 208 are storedwith or associated to an agent identification number. In exemplaryembodiments, N may be 5 files, 100 files, or 1,000; however, these aremerely exemplary numbers. In an embodiment, the N files selected at 20may be further filtered in order to only select audio files in which thespeaker, and thus the identified speaker are easy to differentiate, forexample due to the frequency of the voices of the different speakers. Byselecting only those files in which the acoustic differences between thespeakers are maximized, the acoustic voiceprint model as disclosedherein may be started with files that are likely to be accurate in thespeaker separation. In one embodiment, the top 50% of the selected filesare used to create the acoustic voiceprint, while in other embodiments,the top 20% or top 10% are used; however, these percentages are in noway intended to be limiting on the thresholds that may be used inembodiments in accordance with the present disclosure.

In a still further embodiment, a diarization or transcription of theaudio file is received and scored and only the highest scoring audiofiles are used to create the acoustic voiceprint model. In anembodiment, the score may exemplarily be an automatedly calculatedconfidence score for the diarization or transcription. Such automatedconfidence may exemplarily, but not limited to, use an auto correctionfunction.

Each of the files selected at 206 are processed through a diarization at210. The diarization process may be such as is exemplarily disclosedabove with respect to FIG. 1. In an embodiment, the diarization at 210takes each of the selected audio files and separates the file into aplurality of segments of speech separated by non-speech. In anembodiment, the plurality of speech segments are further divided suchthat each segment has a high likelihood of containing speech sectionsfrom a single speaker. Similar to the blind diarization described above,the diarization at 210 can divide the audio file into segments labeledas a first speaker and a second speaker (or in some embodiments morespeakers) at 212.

At 214 the previously identified speaker segments from the plurality ofselected audio files are clustered into segments that are similar to oneanother. The clustering process can be done directly by matchingsegments based upon similarity to one another or by clustering thespeaker segments based upon similarities to a group of segments. Theclustered speaker segments are classified at 216. Embodiments of thesystem and method use one or more metrics to determine which clusters ofspeaker segments belong to the customer service agent and which speakersegment clusters belong to the customers with whom the customer serviceagent was speaking. In one non-limiting embodiment, the metric ofcluster size may be used to identify the segment clusters associatedwith the customer service agent as larger clusters may belong to thecustomer service agent because the customer service agent is a party ineach of the audio files selected for use in creating a model at 206.While it will be recognized that other features related to the agent'sscript, delivery, other factors related to the customer service callsthemselves may be used as the classifying metric.

At 218 an acoustic voiceprint model for the identified speaker,exemplarily a customer service agent is built using the segments thathave been classified as being from the identified speaker. At 220 abackground voiceprint model that is representative of the audio producedfrom speakers who are not the identified speaker is built from thosespeech segments identified to not be the identified speaker, and thusmay include the other speakers as well as background noise.

Therefore, in some embodiments, the acoustic voiceprint model, such asexemplarily used with respect to FIG. 1 described above, includes bothan identified speaker voiceprint 222 that is representative of thespeech of the identified speaker and a background voiceprint 224 that isrepresentative of the other speaker with whom the identified speakerspeaks, and any background noises to the audio data of the identifiedspeaker.

It will be recognized that in embodiments, the creation of the acousticvoiceprint model 202 may be performed in embodiments to create anacoustic voiceprint model for each of a plurality of identified speakersthat will be recorded and analyzed in the diarization method of FIG. 1.Exemplarily in these embodiments, the identified speakers may be aplurality of customer service agents. In some embodiments, each of thecreated acoustic voiceprint models are stored in a database of acousticvoiceprint models from which specific models are accessed as describedabove with respect to FIG. 1, exemplarily based upon an identificationnumber in metadata associated with audio data.

In further embodiments, the processes at 202 may be performed at regularintervals using a predefined number of recently obtained audio data, ora stored set of exemplary audio files. Such exemplary audio files may beidentified from situations in which the identified speaker isparticularly easy to pick out in the audio, perhaps due to differencesin the pitch or tone between the identified speaker's voice and theother speaker's voice, or due to a distinctive speech pattern orcharacteristic or prevalent accent by the other speaker. In still otherembodiments, the acoustic voiceprint model is built on an ad hoc basisat the time of diarization of the audio. In such an example, theacoustic model creation process may simply select a predetermined numberof the most recent audio recordings that include the identified speakeror may include all audio recordings within a predefined date thatinclude the identified speaker. It will be also noted that once theaudio file currently being processed has been diarized, that audiorecording may be added to the repository of audio files 208 for trainingof future models of the speech of the identified speaker.

204 represents an embodiment of the use of the acoustic voiceprint modelas created at 202 in performing a speaker diarization, such asrepresented at 114 in FIG. 1. Referring back to FIG. 2, at 226 new audiodata is received. The new audio data received at 226 may be a stream ofreal-time audio data or may be recorded audio data being processed.Similar to that described above with respect to 110 and 112 in FIG. 1,the new audio data 226 undergoes diarization at 228 to separate the newaudio data 226 into segments that can be confidently tagged as being thespeech of a single speaker, exemplarily a first speaker and a secondspeaker. At 230 the selected acoustic voiceprint 222 which may includebackground voiceprint 224, is compared to the segments identified in thediarization at 228. In one embodiment, each of the identified segmentsis separately compared to both the acoustic voiceprint 222 and to thebackground voiceprint 224 and an aggregation of the similarities of thefirst speaker segments and the second speaker segments to each of themodels is compared in order to determine which of the speakers in thediarized audio file is the identified speaker.

In some embodiments, the acoustic voiceprint model is created from acollection of audio files that are selected to provide a sufficientamount of audio data that can be confidently tagged to belong only tothe agent, and these selected audio files are used to create the agentacoustic model. Some considerations that may go into such a selectionmay be identified files with good speaker separation and sufficientlength to provide data to the model and confirm speaker separation. Insome embodiments, the audio files are preprocessed to eliminatenon-speech data from the audio file that may affect the backgroundmodel. Such elimination of non-speech data can be performed by filteringor concatenation.

In an embodiment, the speakers in an audio file can be represented by afeature vector and the feature vectors can be aggregated into clusters.Such aggregation of the feature vectors may help to identify thecustomer service agent from the background speech as the feature vectorassociated with the agent will aggregate into clusters more quickly thanthose feature vectors representing a number of different customers. In astill further embodiment, an iterative process may be employed whereby afirst acoustic voiceprint model is created using some of the techniquesdisclosed above, the acoustic voiceprint model is tested or verified,and if the model is not deemed to be broad enough or be based uponenough speaker segments, additional audio files and speaker segments canbe selected from the repository and the model is recreated.

In one non-limiting example, the speaker in an audio file is representedby a feature vector. An initial super-segment labeling is performedusing agglomerative clustering of feature vectors. The feature vectorsfrom the agent will aggregate into clusters more quickly than thefeature vectors from the second speaker as the second speaker in each ofthe audio files is likely to be a different person. A first acousticvoiceprint model is built from the feature vectors found in the largestclusters and the background model is built from all of the other featurevectors. In one embodiment, a diagonal Gaussian can be trained for eachlarge cluster from the super-segments in that cluster. However, otherembodiments may use Gaussian Mixture Model (GMM) while still furtherembodiments may include i-vectors. The Gaussians are then merged where aweighting value of each Gaussian is proportionate to the number ofsuper-segments in the cluster represented by the Gaussian. Thebackground model can be comprised of a single diagonal Gaussian trainedon the values of the super segments that are remaining.

Next, the acoustic voiceprint model can be refined by calculating alog-likelihood of each audio file's super-segments with both theacoustic voiceprint and background models, reassigning thesuper-segments based upon this comparison. The acoustic voiceprint andbackground models can be rebuilt from the reassigned super-segments inthe manner as described above and the models can be iteratively createdin the manner described above until the acoustic voiceprint model can beverified.

The acoustic voiceprint model can be verified when a high enough qualitymatch is found between enough of the sample agent super-segments and theagent model. Once the acoustic voiceprint model has been verified, thenthe final acoustic voiceprint model can be built with a single fullGaussian over the last super-segment assignments from the application ofthe acoustic voiceprint model to the selected audio files. As notedabove, alternative embodiments may use Gaussian Mixture Model (GMM)while still further embodiments may use i-vectors. The background modelcan be created from the super-segments not assigned to the identifiedspeaker. It will be recognized that in alternative embodiments, aninstitution, such as a call center, may use a single background modelfor all agents with the background model being updated in the mannerdescribed above at periodic intervals.

Embodiments of the method described above can be performed orimplemented in a variety of ways. The SST server, in addition toperforming the LVCSR, can also perform the diarization process. Anotheralternative is to use a centralized server to perform the diarizationprocess. In one embodiment, a stand-alone SST server performs thediarization process locally without any connection to another server forcentral storage or processing. In an alternative embodiment, the STTserver performs the diarization, but relies upon centrally stored orprocessed models, to perform the initial transcription. In a stillfurther embodiment, a central dedicated diarization server may be usedwhere the output of many STT servers are sent to the centralizeddiarization server for processing. The centralized diarization servermay have locally stored models that build from processing of all of thediarization at a single server.

FIG. 4 is a flow chart that depicts an exemplary embodiment of a method400 of performing a blind diarization. The method may exemplarily becarried out within the method 100 as described above, or in anotherapplication of blind diarization. The method 400 begins with audio data402. The audio data 402 may be streaming audio captured and processed inreal-time or near-real-rime, or in other embodiments may be a previouslyacquired and stored audio file. In an embodiment, the audio data is amono audio file.

A voice-activity detector (VAD) is used at 404 to identify non-speechsegments and the audio file is segmented into utterances that areseparated by the identified non-speech segments. In an embodiment, theaudio data is segmented into a series of overlapping frames exemplarily20-25 milliseconds in length; however, this is not intended to belimiting on the scope of the disclosure. In an exemplary embodiment of aspeech-processing system, a 20-25 millisecond frame is processed every10 milliseconds. Such speech frames are long enough to performmeaningful spectral analysis and capture the temporal acousticcharacteristics of the speech signal, yet they are short enough to givefine granularity of the output. In an embodiment, the VAD segments theaudio data into utterances by identifying segments of the audio datathat includes speech from segments of non-speech on a frame-by-framebasis. An audio frame may be identified as speech or non-speech basedupon a plurality of characteristics or probabilities exemplarily basedupon mean energy, band energy, peakiness, or residual energy; however,it will be recognized that alternative characteristics or probabilitiesmay be used in alternative embodiments. To guarantee the robustness ofthe following steps, it is possible to ignore very short utterances.Therefore, the set of sufficiently long utterances is denoted as U₁, U₂,. . . , U_(K) (wherein K is the initial number of utterances). The kthutterance is defined by its start time and its end time U_(k)=

s_(k), e_(k)

.

Acoustic features are extracted at 406 for the entire conversation

₁,

₂, . . . ,

_(T) (wherein T is the total number of frames). The sequence of featurevectors corresponding to the kth utterance is therefore

_(s) _(k) , . . . ,

_(e) _(k) . Having segmented the input signal into frames, thediarization problem becomes discrete and can be viewed as a Markovprocess, where the attribution of a frame to a certain speaker (or theclassification of the frame as silence or background noise) depends onlyon the previous frame and the acoustic characteristics of the frameitself. The extraction of acoustic features at 406 provides thisinformation for the diarization process.

While many types of acoustic features may be extracted, in an exemplaryembodiment, the acoustic features are perceptive linear predictiveanalytics (PLP) as described in: Hermansky H. “Perceptual LinearPredictive (PLP) analysis of speech” in Journal of the AcousticalSociety of America, 87(2), pages 1738-1752. B, which is incorporated byreference in its entirety. In an exemplary embodiment as will bedescribed in further detail herein, the extracted acoustic features areMel-frequency cepstral coefficients (MFCC) for each frame. The MFCC'sare used to model acoustic characteristics of the different speakers.The computation of MFCC is exemplary described in further detail in(Mermelstein P. “Distance measures for speech recognition, psychologicaland instrumental,” in Pattern Recognition and Artificial Intelligence,Chen C. H. (Editor), pages 374-388; Academic, New York (1976)) which ishereby incorporated by reference in its entirety. Different speakers arethen characterized by different multi-dimensional distributions of theirMFCC features, exemplarily in a manner as described below.

The MFCC features extracted from each frame are given as a vector ofreal values of some fixed dimension d. Since the distribution of thefeature vectors may be very complex, it is more convenient toapproximate it as a combination of simpler distributions. The Gaussianmixture model (GMM) is a commonly used representation for ad-dimensional distribution.

A multivariate normal distribution (a.k.a. Gaussian distribution) of avector of d random variables,

=(x₁, . . . , x_(d)), is characterized by the probability densityfunction:

${f\left( \overset{\rightharpoonup}{x} \right)}=={\frac{1}{\sqrt{\left( {2\; \pi} \right)^{d} \cdot {\det (\Sigma)}}} \cdot {\exp \left( {{- \frac{1}{2}} \cdot \left( {\overset{\rightharpoonup}{x} - \overset{\rightharpoonup}{\mu}} \right)^{T} \cdot \Sigma^{- 1} \cdot \left( {\overset{\rightharpoonup}{x} - \overset{\rightharpoonup}{\mu}} \right)} \right)}}$

Where

=(E(x₁), . . . , E(x_(d))) is the expectancy vector and Σ=(cov(x_(i),x_(j)))_(i,j) is the covariance matrix. One can obtain the likelihood ofa given random vector with respect to a Gaussian distribution by takingthe natural logarithm of the probability density function:

L(

)=ln(f(

))=−1/2·(ln((2π)^(d)·det(Σ))+(

−

)^(T)·Σ⁻¹·(

−

))

In case the random variables are independent (as usually is the case forcepstral coefficients), the covariance matrix becomes diagonal, so thedensity function can be simplified by using the variance vector {rightarrow over (σ)}²=(var(x₁), . . . , var(x_(d))):

${L\left( \overset{\rightharpoonup}{x} \right)} = {{- \frac{1}{2}} \cdot \left( {{\ln \left( {\left( {2\; \pi} \right)^{d} \cdot {\prod\limits_{i = 1}^{d}\; \sigma_{i}^{2}}} \right)} + {\sum\limits_{i = 1}^{d}\; \frac{\left( {x_{i} - \mu_{i}} \right)^{2}}{\sigma_{i}^{2}}}} \right)}$

A GMM comprises a set of n Gaussians and their probabilities p₁, . . . ,p_(n) (with Σ_(k=1) ^(K)p_(n)=1). The likelihood of a random vector withrespect to such a GMM is given by (we denote by a⊕b the operation offaddition in the log domain ln(e^(a)+e^(b))):

G(

)=[ln(p ₁)+L ₁(

)]⊕[ln(p ₂)+L ₂(

)]⊕ . . . ⊕[ln(p _(n))+L _(n)(

)]

In order to represent the initial utterances U₁, U₂, . . . , U_(K),which are not real-valued vectors, and there is no natural distancemetric defined on them, using real-valued vectors of a smallerdimension, an approach based on diffusion map embedding has beendeveloped. Diffusion map embedding is generally described by (Coifman R.R., Lafon S. “Diffusion maps”. Applied and Computational HarmonicAnalysis 21: 5-30 (2006)), which is herein incorporated by reference inits entirety.

A large set of n Gaussians representing these feature vectors of theentire audio data is constructed at 408. A possible way to constructsuch a set is to use the k-means algorithm on the set of featurevectors. We refer to this set of Gaussians as the universal model.

Next, at 410 for each utterance (U_(k)) an utterance model isconstructed that represents the distribution of the feature vectors inthat utterance. In an exemplary embodiment, the utterance model is a GMM(Gk) Each GMM is based on the n Gaussians of the universal modelconstructed in the previous step, with its mixture probabilitiescomputed using the following formula (for each 1≤i≤n):

$p_{i}^{(k)} = {\frac{1}{e_{k} - s_{k} + 1} \cdot {\sum\limits_{t = s_{k}}^{e_{k}}\; {\exp \left( {{L_{i}\left( {\overset{\rightharpoonup}{x}}_{t} \right)} - \left\lbrack {{L_{1}\left( {\overset{\rightharpoonup}{x}}_{t} \right)} \oplus \ldots \oplus {L_{n}\left( {\overset{\rightharpoonup}{x}}_{t} \right)}} \right\rbrack} \right)}}}$

Once each utterance is characterized by the vector of mixtureprobabilities of its GMM, a distance metric between the utterances isdefined. This distance can be used to identify between speakers.Conceptually, each speaker has a unique combination of acoustic featuresreflected in the GMM and the distance metrics between the GMMs highlightthese differences. In an embodiment, the distance metric between a pairof utterances (e.g. U_(j) and U_(k)) is the Euclidean distance betweenthe probabilities vector of the utterances (U_(j) and U_(k)) respectiveGMMs G_(j) and G_(k):

${\delta \left( {U_{j},U_{k}} \right)} = \sqrt{\sum\limits_{i = 1}^{n}\; \left( {p_{i}^{(j)} - p_{i}^{(k)}} \right)^{2}}$

Next, at 412, a process of embedding is performed in order to aid in theidentification and separation of speakers by creating additionalmathematical separation between the GMMs of utterances that are lesssimilar. By mathematically separating dissimilar GMMs, the computedEuclidean distance will be greater, drawing sharper contrast betweenfigure clusters. A more detailed embodiment of a process of embedding isdescribed herein in further detail with respect to FIG. 6.

At 414 clustering is used to identify those utterances having similaracoustic features. In one exemplary embodiment, the clustering at 414 ismean-shift clustering, although it is recognized that any clusteringmethod that does not assume a priori knowledge of the number of clustersmay be used, including, but not limited to hierarchical clustering. Anexemplary embodiment of mean-shift clustering is disclosed by (Cheng Y.“Mean shift, mode seeking, and clustering”. IEEE Transactions on PatternAnalysis and Machine Intelligence 17(8): 790-799 (1995)), which isherein incorporated by reference in its entirety. In an embodiment, themean-shift clustering algorithm automatically finds the most suitablenumber of clusters for its input data set. The mean-shift algorithmaccepts a set of real-valued vectors of dimension

, denoted

₁,

₂, . . . ,

_(K)∈

, and computes a subdivision into N clusters based on the Euclideandistance between pairs of data vectors, where N is not known in advance.In an embodiment, input data vectors

₁,

₂, . . . ,

_(K) represent the initial utterances U₁, U₂, . . . , U_(K) and N is thenumber of speakers in the recorded conversation. The subdivisioncomputed by the mean-shift algorithm defines the initial association ofutterances to each of these N speakers. Each of the identified Nclusters can be used as a model of each speaker constructed at 416.

Having partitioned the initial utterances into clusters, by maximizingthe differences between their acoustic features and mean-shiftclustering to form speaker models at 416 a hidden Markov model (HMM) ofthe clustered speakers is created at 418. FIG. 5 is an exemplaryembodiment of a state diagram modeling a conversation between N speakersin the form of a HMM. The HMM includes states labeled S₁, S₂ . . . S_(N)represent the speakers, and are each associated with cluster ofutterances obtained as described above. The HMM state labeled Brepresents the background and non-speech portions of the conversation.It is possible to associate the background and non-speech portions witha GMM that is computed using the feature vectors extracted from theaudio portions that are classified as non-speech as described above.

As continuous speech and non-speech segments are expected, theprobabilities associated with the self-loops of the HMM should be veryhigh. Since each utterance is exemplarily 20 milliseconds long, asignificant number of utterances associated with the same state (S₁, S₂,S_(N), B) will likely occur in a row before a transition is made toanother speaking state. In an exemplary embodiment each self-loop isgiven an initial probability p that is close to one. The probabilitiesof the other arcs, which represent transitions between states, in anembodiment may initially equal

$\frac{1}{N}{\left( {1 - p} \right).}$

The initial HMM parameters are updated at 420, exemplarily through theuse of Baum-Welch re-estimation. This update may exemplary be performedusing the complete sequence of feature vectors x₁, x₂, . . . , x_(T). Ina non-limiting embodiment, this updating can be performed with one ormore iterations of the Baum-Welch algorithm as described in (Baum L. E,Petrie T., Soules G., Weiss N., “A maximization technique occurring inthe statistical analysis of probabilistic functions of Markov chains”.The Annals of Mathematical Statistics 41(1), 164-171 (1970)), which ishereby incorporated by reference in its entirety.

The best path corresponding to x₁, x₂, . . . , x_(T) in the resultingHMM is decoded at 422. In an non-limiting embodiment this may beperformed using the Viterbi algorithm as described in Viterbi A. J.,“Error bounds for convolutional codes and an asymptotically optimumdecoding algorithm”. IEEE Transactions on Information Theory 13(2):260-269 (1967), which is hereby incorporated by reference in itsentirety. The Viterbi algorithm outputs a best path as a sequence of thespeaker states (S₁, S₂, S_(N), B) and time lengths at these states thatbest corresponds to the underlying signal. The identified best path isanalyzed to locate sufficiently long sequences of traversals of eitherS₁ or S₂, and to create output utterances W₁, W₂ , . . . , W_(M). Anoutput utterance W_(m)=

s_(m), e_(m), l_(m)

is also given a label l_(m)∈{S₁ . . . S_(N)} that corresponds to thebest-path sub-sequence that has induced it.

In other words, the Viterbi algorithm is performed on a per-frame basis;namely, given a feature sequence

₁, . . . ,

_(T) that represents the feature vectors of a single utterance, defineM[k,t] as the maximal score of reaching the k'th state after the first tfeature vectors

₁, . . . ,

_(t). Thus for each k, let: M[k,0]=0 and for each 1≤t≤T, let:

${{M\left\lbrack {k,t} \right\rbrack} = {\max\limits_{1 \leq j \leq m}\left\{ {{M\left\lbrack {j,{t - 1}} \right\rbrack} + {\omega \left( {j,k} \right)} + {S_{k}\left( {\overset{\rightharpoonup}{x}}_{t} \right)}} \right\}}},$

in which S_(k)(

_(t)) is the emission log-likelihood of the feature vector

_(t) from the GMM S_(k), and ω(j, k) is the logarithmic weight of thetransition from S_(j) to S_(k). Then locate the overall maximal scorefor the entire sequence, namely find

$\max\limits_{k}{M\left\lbrack {k,T} \right\rbrack}$

and trace back the best path, which indices the segmentation, viaback-pointers.

FIG. 6 is a flow chart that depicts an exemplary embodiment of a moredetailed process carried out during embodiments of a method of blinddiarization with an arbitrary number of speakers, particularly, themethod 500 depicted in FIG. 6 depicts an exemplary embodiment of stepsthat may be carried out in forming the embedding at 412 of the method400 as found in FIG. 4. The method 500 begins by receiving calculateddistances between the utterances 502. In an embodiment, the distancesare Euclidean distances between the probability vectors of theutterances of the N Gaussians of the universal model.

At 504, a K×K affinity matrix D is constructed based upon the distancemetric given by the following equation in which σ is a parameter:

$D_{jk} = {\exp \left( {- \frac{\delta^{2}\left( {U_{j},U_{k}} \right)}{\sigma}} \right)}$

Next, at 506, a stochastic matrix W is computed form the K×K affinitymatrix D. the stochastic matrix W can be computer using the followingequation:

$W_{jk} = \frac{D_{jk}}{\sum\limits_{i = 1}^{K}\; D_{ji}}$

Since W is a stochastic matrix, the largest eigenvalue of the matrixequals 1. At 508, the next

largest eigenvalues of the matrix W, denoted λ₁, . . . ,

, and their corresponding eigenvectors

₁, . . . ,

are computed from the stochastic matrix W.

Finally, at 510 the embedding of the utterances U₁, U₂, . . . , U_(K)into

-dimensional vectors (

₁,

₂, . . . ,

_(K)∈

) is computed. The

-dimensional vectors (

₁,

₂, . . . ,

_(K)∈

), of which α is a parameter, are defined as follows:

_(k,i)=(λ_(i))^(α)·

_(k,i)

The embedded utterances can then be processed using mean-shiftclustering as described above with respect to FIG. 4.

The method as described above is thus capable of recognizing anarbitrary number of speakers in a conversation. This produces a numberof distinct advantages. The accuracy of the blind diarization issignificantly higher, as the algorithm is not forced to separate theconversation between two speakers. Problematic utterances, such as, butnot limited to, background talks or cross-talks, tend to be clustered asa separate speaker (or sometimes several speakers). When transcribed,these segments tend to have low transcription score. Therefore, it ispossible to disqualify such low-quality clusters that do not representtrue speakers. In embodiments wherein the conversation needs to be fullytranscribed, and not just diarized, it is possible to benefit from theaccurate diarization and use per-speaker model adaptation, whichincreases the accuracy of transcription as well.

The diarization results may be used to identify a specific speaker, someof the speakers or all speaker, in embodiments wherein the voicecharacteristics of these speakers (e.g. their voice characteristics) areknown to the system. In embodiments, it is possible to detect anirregular event in the conversation. Such irregular events may include,but are intended to by merely exemplary, call transfers, speakerswitches, or joining of an additional speaker to a conference call. Inembodiments, diarization results can be further used to derive moreaccurate statistics out of each conversation such as numbers ofspeakers, speaker total duration, or a speaker histogram. Certainanomalies can be detected using these statistics, such allowing moreaccurate analysis of the conversation by an expert system. Asnon-limiting examples, calls with a single speaker may be discarded orcalls with unusual behaviors may be excluded. In embodiments, thediarization process also determines the speakers' change points during aconversation. Such information is highly valuable in analyzing theconversation flow.

However, the blind diarization process described above is not withoutpotential drawbacks. For example, in some known cases VAD filtering hasbeen seen to fail to filter out non-speech segments, noises or music—soas a result too many speakers are created by the blind-diarizationalgorithm. In such a case, the segments of one of the speakers may bewrongly split between two false speakers. In other cases, two truespeakers may be misclassified as a single speaker while the otherspeaker comprises mainly non-speech segments.

Another potential drawback of the blind diarization process is thatbecause the Viterbi process is performed on a per-frame basis, the valueof ω(j, k) for j=k must be significantly higher than the values for j≠kin order to avoid very frequent transitions among speakers. Thus theblind diarization process sometimes fails to detect short utterances ifthe short utterances are interleaved with longer utterances of anotherspeaker due to these co values.

To address the drawbacks above, a second-pass blind diarization process,which can be added to the blind diarization process described above, isdisclosed herein. In general, The because VOD filtering in certain casesis not accurate enough, one can use the results of a second-pass LVCSRdecoder, which are significantly more accurate, to obtain much morereliable filtering of non-speech segments as compared to only using VODfiltering. The number of speakers and the speaker GMMs can then beconstructed based on the more accurate speech segments. However, as thesecond-pass decoding is a time-consuming process, in certain embodimentssecond-pass decoding is not repeated after the speakers are identified.Instead, the decoded words are assigned to the speakers in a processcalled word-level segmentation.

FIG. 7 is a flow chart that depicts an exemplary embodiment of a method700 of performing second-pass blind diarization. The method 700 mayexemplary be carried out within the method 400, for example after step422, or in other suitable applications like blind diarization. Themethod 700 begins with a second-pass filtration process that uses theresults of a second-pass LVCSR decoder to filter non-speech segmentsfrom the initial segments classified by the VAD detector as containingspeech 702.

In an exemplary embodiment, the second-pass filtering process 702 beingswith each VAD segment being decoded using for example an LVCSR decoder.The sequence of output words and non-speech symbols from the LVCSRdecoder is then analyzed, the non-speech parts are discarded and thesegment is refined accordingly. Thus for example, if the LVCSR decoderoutput on a certain segment was “<SIL> GOOD MORNING <SIL> <VN> <SIL> YESYES I COULD NOT GET ANY INFORMATION THERE”, then the segment is splitinto two, the first sub-segment corresponding to the word sequence “GOODMORNING”, and the other sub-segment corresponds to “YES YES I COULD NOTGET ANY INFORMATION THERE”. Segments that mainly contain non-speechsymbols may be completed discarded.

The second-pass blind diarization 700 method then creates speaker modelsby feeding the resulting sub-segments into a clustering algorithm 704,for example, feeding the resulting sub-segments into the mean-shiftalgorithm described in detail above. The output of the clusteringalgorithm are speaker models, for example, GMMs that are based only onthe “clean” speech segments, which can be denoted as Ŝ₁, . . . , Ŝ_(m),(m′ is the number of speakers, as determined by the second invocation ofthe mean-shift algorithm).

The second-pass blind diarization 700 method then performs word-levelsegmentation 706 which uses the speaker models, for example, GMMs Ŝ₁, .. . , Ŝ_(m), to construct an HMM. The HMM can be constructed similar tothe topology described above and shown in FIG. 5. Given a word sequenceW₁, . . . , W_(N) that have been output from the second-pass LVCSRdecoder for the relevant utterances, words are then assigned words tospeakers, in which the start time-frames of each word can be given ast₀, . . . , t_(N). Again the Viterbi algorithm is used to perform thistask, but unlike the blind diarization process described above, here thecomputations are performed on a word basis; namely, given a wordsequence W₁, . . . , W_(N), define M′[k,t] as the maximal score ofreaching the k'th state after the first n words W₁, . . . , W_(n). Thusfor each k, let: M′[k, 0]=0 and for each 1≤n≤N, let:

${{M^{\prime}\left\lbrack {k,n} \right\rbrack} = {\max\limits_{1 \leq j \leq m^{\prime}}\left\{ {{M^{\prime}\left\lbrack {j,{n - 1}} \right\rbrack} + {\pi \left( {j,k} \right)} + \overset{\_}{{\hat{S}}_{k}\left( w_{n} \right)}} \right\}}},$

in which π(j, k) is the logarithmic weight of the transition from S_(j)to S_(k) and Ŝ_(k)(w_(n)) is the averaged emission log-likelihood of thenth word from the GMM Ŝ_(k), defined as

$\overset{\_}{{\hat{S}}_{k}\left( w_{n} \right)} = {\frac{1}{t_{n} - t_{n - 1}} \cdot {\sum\limits_{\tau = t_{n - 1}}^{t_{n} - 1}\; {{{\hat{S}}_{k}\left( {\overset{\rightharpoonup}{x}}_{\tau} \right)}.}}}$

Then locate the overall maximal score for the entire sequence, namelyfind

$\max\limits_{k}{M^{\prime}\left\lbrack {k,T} \right\rbrack}$

and trace back the best path, which indices the segmentation, viaback-pointers. This path determines the association of words tospeakers.

Utilizing a second-pass blind diarization subsequent to a first-passblind diarization can provide several advantages. For example, theresults of a first-pass blind diarization are only used by thesecond-pass blind diarization to perform speaker adaptation of theacoustic features before sending them to the second-pass decoding. Evenconsidering the drawbacks of the first-pass blind diarization process,these results are accurate enough for the feature-adaptation purpose.The second-pass filtering of non-speech segments is far more accuratethat the first-pass filtering, which can lead to a more accuratedetermination of the correct number of speakers and, in many cases, tothe creation of better speaker models.

Furthermore, word-level segmentation is more reliable, as classificationis performed using broader support as opposed to a per-frame basis.Moreover, since the transition weight π(j, k) should not be tiny forj≠k, the second-pass blind diarization now makes it possible to detectshort utterances of one speaker that are interleaved between the speechsegments of another speaker.

FIG. 8 is a flow chart that depicts an exemplary embodiment of a method800 of creating acoustic signatures for a speaker from multiple recordedaudio sessions that can be based only on statistical models of thespeakers in each of a set of recorded sessions. The method 800 can becarried out in isolation or in embodiments where diarization with anarbitrary number of speakers is being performed. For example, the method800 may be carried out in building the acoustic voiceprint model at 218of the method 200 as found in FIG. 2.

The method 800 includes a classification procedure 802 and an acousticsignature generation procedure 804. The classification procedure 802seeks to identify which speaker models correspond to the common speakerand which models correspond to other speakers. Given a training setcontaining K sessions, each comprising several speaker models, speakermodels of the nth session can be denoted by S₁ ^((n)), . . . , S_(K)_(n) ^((n)). Each model can be characterized by its occupancy, which isproportional to the number of feature vectors used to construct themodel; the model occupancies of the nth session can be denoted by γ₁^((n)), . . . , γ_(K) _(n) ^((n)).

In some embodiments, the classification procedure 802 is performed byconstructing an undirected similarity graph

having vertices correspond to the speaker models of all n sessions. Ingraph

, two vertices S_(i) ^((m)) and S_(i) ^((n)) are said to be connected byan edge if the following holds

$j = {{\underset{1 \leq k \leq K_{n}}{argmin}{{\delta \left( {S_{i}^{(m)},S_{k}^{(n)}} \right)}\bigwedge i}} = {\underset{1 \leq k \leq K_{m}}{argmin}{{\delta \left( {S_{k}^{(m)},S_{j}^{(n)}} \right)}.}}}$

Note that the maximal possible degree of a vertex in

is (n−1). The distance δ(S₁, S₂) between a pair of GMMs S₁ and S₂ ofdimension d, may be defined as follows: If both GMMs are defined over acommon set of Gaussians, and differ only by their mixturesprobabilities, we have

${{\delta \left( {S_{1},S_{2}} \right)} = {\sum\limits_{i = 1}^{m}\; \left( {p_{i}^{(1)} - p_{i}^{(2)}} \right)^{2}}},$

if the GMMs do not share a common set of Gaussians, define:

δ(S ₁ , S ₂)=[(ln p ₁ ⁽¹⁾ +S ₂(

₁ ⁽¹⁾))⊕ . . . ⊕(ln p _(m) ₁ ⁽¹⁾ +S ₂(

_(m) ₁ ⁽¹⁾))]++[(ln p ₁ ⁽²⁾ +S ₁(

₁ ⁽²⁾))⊕ . . . ⊕(ln p _(m) ₂₁ ⁽²⁾ +S ₁(

_(m) ₂ ⁽²⁾))]

The speaker models can then be classified according to the degree oftheir corresponding vertex in

. Given two thresholds 0<τ_(min)<τ_(max)<1, S_(i) ^((m)) is classifiedas a common speaker model if S_(i) ^((m))>τ_(max)·(n−1), S_(i) ^((m)) isclassified as a general speaker model if S_(i) ^((m))<τ_(min)·(n−1),otherwise S_(i) ^((m)) is unclassified.

In regards to the acoustic signature generation procedure 804, given aset of L GMMs, denoted S₁, . . . , S_(L), and their occupancies, denotedγ₁, . . . , γ_(L), a super-GMM is then constructed that captures theentire set of L GMMs. If all GMMs are defined over a common set of mGaussians, the resulting super-GMM will also be defined over thesecommon Gaussians, and its mixture probabilities {circumflex over (p)}₁,. . . , {circumflex over (p)}_(m) are given by:

${\hat{p}}_{i} = {\sum\limits_{j = 1}^{L}\; {\frac{\gamma_{j}}{\sum\limits_{k = 1}^{L}\; \gamma_{k}} \cdot p_{i}^{(j)}}}$

However, if the set of Gaussians is not shared, a large set of N randomfeature vectors are generated. Since a GMM S represents a d-dimensionaldistribution, it is possible to generate a set of J random vectors

₁, . . . ,

_(N) that are distributed according to this distribution in thefollowing manner:

-   -   For each 1≤j≤J:        -   Pick up a mixture index 1≤i≤m, such the probability of            picking a mixture is proportional to its probability p_(i).        -   Generate a vector            _(j) of d independent random variables with standard normal            distribution, namely            _(j,k)˜Normal(0,1) for 1≤k≤d.        -   Using the mean vector            _(i) and the covariance matrix Σ_(i) of the selected            Gaussian, compute:

_(j)=Σ_(i) ⁻¹·(

_(j)+

_(i)).

Accordingly, if the set of Gaussians is not shared, a large set of Nrandom vectors are generated using the procedure described above bycomputing J₁, . . . , J_(L) such that:

$J_{i} = \left\lfloor {{\frac{\gamma_{i}}{\sum\limits_{k = 1}^{L}\; \gamma_{k}} \cdot N} + \frac{1}{2}} \right\rfloor$

In particular, for each 1≤i≤L, generate J_(i) random vectors from theGMM S_(i).

A super GMM is then created by training a Gaussian mixture model overthese random feature vectors. The number of mixtures in this super-GMMmay be given by a parameter k, in which case the model can be trained byiterative Gaussian splitting or by clustering the random data vectorsusing the k-means algorithm. Alternatively, the resulting number ofmixtures can be determined by the data if we use bottom-up clustering ormean-shift clustering.

In other words, executing the classification procedure 802 obtains twosets of GMMs. In particular, a set of common speaker GMMs, which can bedenoted

_(C), and a set of generic speaker GMMs, which can be denoted

_(G). Then two super-GMMs are constructed, A_(C) from

_(C) and A_(G) from

_(G) 804, the acoustic signature for the common speaker is given as thesuper-model pair

A_(C), A_(G)

.

Note that given a session that is not included in the training set, itis possible to collect the set X of all feature vectors from segmentsthat are judged to belong to the same speaker. In such a case, given anacoustic signature

A_(C), A_(G)

, the likelihood that this speaker corresponds to this signature can beexpressed as:

${\frac{1}{X} \cdot {\sum\limits_{\overset{\rightharpoonup}{x} \in X}\; {A_{C}\left( \overset{\rightharpoonup}{x} \right)}}} - {A_{G}\left( \overset{\rightharpoonup}{x} \right)}$

Method 800 provide several advantages over known acoustic signaturecreation processes. For example, method 800 allows one to generate anacoustic signature without the need for processing an entire audio dataor extracting acoustic features from an entire audio data. Method 800only needs to accumulate the speaker models of the training sessions.Speaker models are far more compact and consume less memory or diskspace as compared to audio data. Additionally, it is possible withmethod 800 to generate an acoustic signature even if the common speakeris not present in all sessions of the training set, provided that otherspeakers do not occur frequently in the training sessions.

The functional block diagrams, operational sequences, and flow diagramsprovided in the figures are representative of exemplary architectures,environments, and methodologies for performing novel aspects of thedisclosure. While, for purposes of simplicity of explanation, themethodologies included herein may be in the form of a functionaldiagram, operational sequence, or flow diagram, and may be described asa series of acts, it is to be understood and appreciated that themethodologies are not limited by the order of acts, as some acts may, inaccordance therewith, occur in a different order and/or concurrentlywith other acts from that shown and described herein. For example, thoseskilled in the art will understand and appreciate that a methodology canalternatively be represented as a series of interrelated states orevents, such as in a state diagram. Moreover, not all acts illustratedin a methodology may be required for a novel implementation.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

1. A method of creating an acoustic signature, the method comprising:receiving audio data at a communication interface of a computing systemon a frame by frame basis, wherein at least one frame includes meta dataregarding the audio data; selecting a model to create a speech to texttranscription according to the metadata; creating a speech to texttranscription of the audio data; segmenting the audio data according toidentified word sequences; clustering segments of the audio dataaccording to the identified word sequences; applying an acousticalmatching technique to one of the clusters of identified word sequencesto identify at least one speaker generating at least one of the wordsequences; and tagging identified speakers originating the identifiedword sequences.
 2. A method according to claim 1, further comprisingusing the meta data to select a topical linguistic model to create thespeech to text transcription
 3. A method according to claim 1, furthercomprising filtering out non-speech frames by evaluating envelope energylevel of respective frames and comparing the envelope energy to athreshold energy above which a frame includes an utterance.
 4. A methodaccording to claim 1, further comprising assigning start time frames tothe word sequences, wherein the clustering is further based onrespective time lengths of the word sequences.
 5. A method according toclaim 1, wherein the segmenting further comprises using voice activitydetection to segment the audio data into utterances having a statisticallikelihood of emanating from a single speaker.
 6. A method according toclaim 1, wherein the metadata comprises an identification number for oneor more of the speakers in the audio data.
 7. A method according toclaim 1, wherein the metadata comprises context data selected from thegroup consisting of including a topic, time, date, and location of audiodata origin.
 8. A method for creating a plurality of acoustic signaturesand for performing diarization, comprising: receiving audio data at acommunication interface of a computing system, wherein at least oneframe includes meta data regarding the audio data; selecting a model tocreate a speech to text transcription according to the metadata;creating the speech to text transcription of the audio data inaccordance with the meta data; clustering respective segments of theaudio data according to word sequences; classifying the segments toidentify a set of common speaker Gaussian mixture models (GMMs) and aset of generic speaker GMMs, wherein the classifying includesconstructing an undirected similarity graph having verticescorresponding to a plurality of speaker models of previously recordedaudio sessions in a training set; wherein the classifying furtherincludes determining with a processor in a computing system a degree ofsimilarity between the corresponding vertices in the undirectedsimilarity graph in relation to at least one threshold degree ofsimilarity; generating an acoustic signature by at least: constructing asuper-GMM for the set of common speaker GMMs, and constructing super-GMMfor the set of generic speaker GMMs by generating a set of randomvectors and training a GMM over these random vectors, wherein theacoustic signature for respective common speakers is given as asuper-model pair of the two constructed super-GMMS; and storing thesuper-GMMs in a computing system memory; receiving additional audio dataat the communication interface; identifying a respective common speakerusing the super-model pair; and labeling the additional audio data withan identified common speaker label.
 9. The method according to claim 8,further comprising utilizing a diagonal Gaussian distribution for theclusters to calculate a log likelihood that respective segments arewithin the cluster.
 10. The method according to claim 8, wherein theprerecorded training sets reside on a server.
 11. The method accordingto claim 8, further comprising filtering short utterances as backgroundaudio.
 12. The method according to claim 8, further comprising filteringout short utterances on a time duration basis.
 13. The method accordingto claim 8, further comprising classifying the clusters according toMel-frequency cepstral coefficients (MFCC) for respective frames ofaudio data.
 14. The method according to claim 8, further comprising:determining a cluster of segments to be comprised of respectiveutterances and representing a distribution of feature vectors in therespective utterances; characterizing each feature vector in terms ofits probability of being present in one of the clusters; calculating adistance metric between utterances according to the probability;identifying time between speakers in the audio stream.
 15. The methodaccording to claim 14, further comprising: using distances betweenutterances to construct an affinity matrix based upon respectivedistances; computing a stochastic matrix from the affinity matrix;computing eigenvalues and corresponding eigenvectors of the stochasticmatrix; and computing the embedding of the utterances into dimensionalvectors; identifying embedded utterances in a frame as an additionalspeaker or as additional background audio.
 16. The method according toclaim 8, further comprising using the processor to determine the degreeof similarity by calculating a distance (6) between the correspondingvertices of the speaker models.
 17. A system of creating an acousticsignature, the system comprising: at least one computer connected forcommunication over a network and comprising a processor in datacommunication with memory storing computer readable commands configuredto implement the following steps in a computerized process: receivingaudio data at a communication interface of the computer on a frame byframe basis, wherein at least one frame includes meta data regarding theaudio data; selecting a model to create a speech to text transcriptionaccording to the metadata; creating a speech to text transcription ofthe audio data; segmenting the audio data according to identified wordsequences; clustering segments of the audio data according to theidentified word sequences; applying an acoustical matching technique toone of the clusters of identified word sequences to identify at leastone speaker generating at least one of the word sequences; and taggingidentified speakers originating the identified word sequences.
 18. Amethod according to claim 17, further comprising using the meta data toselect a topical linguistic model to create the speech to texttranscription
 19. A method according to claim 17, further comprisingfiltering out non-speech frames by evaluating envelope energy level ofrespective frames and comparing the envelope energy to a thresholdenergy above which a frame includes an utterance.
 20. A method accordingto claim 17, further comprising assigning start time frames to the wordsequences, wherein the clustering is further based on respective timelengths of the word sequences.